OZG-6239 sendMessage: Use validator

...java/de/ozgcloud/xta/test/app/mapper/ExceptionMapper.java

...ain/java/de/ozgcloud/xta/test/app/model/XtaConstants.java

...java/de/ozgcloud/xta/test/app/server/SendXtaPortImpl.java

...a/de/ozgcloud/xta/test/app/service/XtaMessageService.java

...de/ozgcloud/xta/test/app/validation/RequestValidator.java

.../de/ozgcloud/xta/test/app/mapper/ExceptionMapperTest.java

.../de/ozgcloud/xta/test/app/server/SendXtaPortImplTest.java